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Below is an article posted in the Journal of Etiology and Animal Health about the "Non-Reproductive Long-Term Health Complications of Gonad Removal in Dogs as Well as Possible Causal Relationships with Post-Gonadectomy Elevated Luteinizing Hormone (LH) Concentrations".

Abstract:
 
Throughout most of the developed world, surgical sterilization via gonadectomy has become a common tool for combating the overpopulation of unwanted dogs as well as to eliminate the risk of reproductive diseases in pet dogs.  However, if a surgical sterilization method is chosen that enables a dog to keep its gonads intact while still preventing reproduction, this may avoid the problems discussed in this article.  In the dog as in other normal adult mammals, the hypothalamus secretes gonadotropin-releasing hormone (GnRH), which stimulates the anterior pituitary gland to release of luteinizing hormone. Luteinizing hormone (LH) stimulates the secretion of gonadal steroid hormones (testosterone in males and estrogen/progesterone in females). These gonadal steroid hormones then negatively feedback to the hypothalamus and anterior pituitary to decrease the secretion of GnRH and LH, respectively.  However, in the gonadectomized mammal, there is no negative feedback, which results in supraphysiologic circulating concentrations of LH. In gonadectomized dogs, LH concentrations are more than thirty times the concentrations found in normal adult dogs. Although the main role of LH is for reproductive functions (e.g. ovulation, corpus luteum formation), there are LH receptors present throughout the body, not just limited to the reproductive tract. The purpose of LH receptors in non-reproductive tissues is not known but may induce cell division and stimulate nitric oxide release. With constant activation following gonadectomy, these receptors are up regulated, further magnifying the effects of the extremely high LH concentrations in non-reproductive tissues.  Canine gonadectomy increases the risk of several non-reproductive long-term disorders caused by extremely high LH including obesity, urinary incontinence, urinary calculi, diabetes mellitus, hypothyroidism, hip dysplasia, cranial cruciate ligament rupture, aggressive and fearful behavior, cognitive dysfunction syndrome, prostate adenocarcinoma, transitional cell adenocarcinoma, osteosarcoma, hemangiosarcoma, lymphosarcoma, and mastocytoma. In this review, the relationship between LH receptor activation in these non-reproductive target tissues will be discussed.
 
Read the research paper HERE!